Method of forming side seams for zippered bags or packages

Abstract: A method for manufacturing reclosable plastic bags or packages, wherein sections of zipper profiles are pre-softened at intervals equal in length to the width of the bags or packages to be manufactured. The pre-softening enables the zipper profiles (18,20) to be fused together and completely flationed when a seal bar (32) clamps thereacross to form a side seal area (34) transverse to the zipper.

Description: Background of the Invention 1. Field of the Invention The present invention relates to the manufacture of plastic bags or packages having two plies of thermoplastic sheeting, both plies having closure strips formed or included on their facing inner edges so as to form a sliderless zipper closure for the openings of the bags or packages made therefrom. The plies may be formed of two separate sheets or a single sheet folded over. 2. Description of the Prior Art The present invention relates to improvements in the package-making art and may be practiced, without limitation, in the manufacture of thermoplastic bags and trays of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture and air-tight packages, free from leakage until opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein. The indicated art is fairly well developed, but nevertheless is still susceptible of improvements contributing to increased efficiency and cost effectiveness. One problem that still exists in the production of packages from continuous zipper-equipped sheet material, is the difficult in attaining a satisfactory sealing of the bag or package against leakage, where the zipper and area of film engaged by the zipper extends through the side seal areas separation one bag or package from the next. Document US-A-4812192 discloses a process for manufacturing thermoplastic bags having thickened sections resulting from the presence of zipper closures comprising the steps of: preblocking thermoplastic material in areas of said material to be severed and sealed which are located adjacent to the zipper closure portions thereof; next, blocking said thermoplastic material in areas of said material to be severed and sealed which are located both adjacent to said zipper closure portions and throughout remaining sections thereof to render said thermoplastic material tacky and temporarily stick said multiple plies together in said areas ; preheating said zipper closure portions of said material in said areas thereof to be severed and sealed by applying heat thereto by contacting said zipper closure portions with block like elements preheated within a range of 176,66°C to 287,77°C (350 to 550 °F), and then, contacting all of said areas of said thermoplastic material to be severed and sealed with a heated cutting and sealing element so as to sever all of said multiple plies and concurrently seal said severed margins thereof together. Summary of the Invention The features of the method according to the invention are defined in the appended undependent claim. The present invention is directed at a method for manufacturing plastic bags or packages representing a solution to the above-mentioned problem in the prior art. In its broadent form, the method comprises the step of softening the interlocked male and female profile sections on both the profile surface and the opposite surface as the bag or package is being manufactured at preselected intervals corresponding to the width of the bags or packages being manufactured. The interior softening is accomplished by directing intermittent blasts of hot air through holes provided in insulated tubes used to guide the interlocked profile sections during the manufacture of the packages. This pre-heating of the profiles is at points where side seals are to be provided, and allows the profiles to be sealed together and flattened more readily by the seal bare during the bag making operation. The present invention will now be described in more complete detail below with reference frequently being made to the following figure. Brief Description of Drawings The figure shows an apparatus with which the present invention may be practiced. Detailed Description of the Preferred Embodiment Referring to the Figure, which depicts an apparatus used in manufacturing plastic bags or packages, the apparatus having been modified to do so in accordance with the present invention, plastic sheet material 10 is directed toward a filling tube 12 and associated forming collar 14, which guides the plastic sheet material 10 around the filling tube 12 to form a tube of the plastic sheet material. The fill tube 12 may, for example, be the fill tube of a conventional vertical form fill and seal (VFFS) machine. As this is done, the lateral edges 16 of the plastic sheet material 10 are brought together so that they may ultimately form the two sides of the opening of a plastic bag or package being manufactured on the machine. As the two lateral edges 16 are brought together, a male profile section 18 and a female profile section 20, previously interlocked with one another and provided on the interior surface of the sheet material (i.e. the surface directed toward the fill tube), are continuously guided therebetween on two guide tubes 22. The guide tubes 22, which may have thin rectangular cross sections, each include an internal conduit 24 through which blasts of hot air may be forcibly directed. guide tubes 22 are disposed between the interlocked male profile section 18 and female profile section 20, and on either side of their interlocked parts. At preselected intervals, holes 26,28 through the guide tubes 22 permit hot air to escape in timed blasts upon the interlocked male and female profile sections 18,20. Except for the holes 26,28 the guide tube 22 are insulated. The hot air issuing from the holes 26,28 serves to pre-soften only those portions of the male profile section 18 and female profile section 20 adjacent thereto, those portions ultimately being the locations of side seal areas separating individual bags or packages. Further, the hot air is directed at the actual engaging surfaces of the profiles, rather than at the rear of the profiles as would be the case if air were directed from without rather than from within the package. This permits the profiles to be softened to facilitate their being fused together in a tight seal. In the actual manufacture of plastic bags or packages using the apparatus shown in the Figure, the plastic sheet material 10 is moved incrementally in amounts equal in length to the width of the bags or packages being manufactured. Each time the plastic sheet material 10 is at rest, several actions take place simultaneously. Firstly, blasts of hot air issue from holes 26 in guides 22 to pre-soften adjacent areas of the male profile section 18 and female profile section 20. Secondly, vertical seal bars 30 compress the two lateral edges 16 of the plastic sheet material 10 together and seal them to the male and female profile sections and, if desired, each other outboard of the profile sections. That is, if desired, the vertical seal bars 30, in addition to fusing the zipper to the plastic material may be used to form a seal outboard of the zipper by fusing the edges 16 to each other which must first be cut or otherwise ruptured by the consumer to provide access to the zipper for opening the final bag. Alternatively, a separate vertical seal bar (not shown) may be provided for joining the edges of the plastic sheet. Thirdly, as hot air issues from holes 26 hot air also issues from holes 28 to again presoften adjacent areas of the male and female profile sections 18,20. Holes 26 and holes 28 being separated by an amount equivalent to two bag or package widths. And fourthly, horizontal seal bars 32 clamp completely across the plastic sheet material 10 to form a side seal area 34 and which is also cut to form separate plastic bags or packages. It should be appreciated that whereas the zipper in the preferred embodiment is provided separate from the plastic sheet material, the profile sections could have been formed integrally with the plastic sheet material or formed separate from the plastic sheet material but attached to the plastic sheet material before the bag making machine or at the bag making machine upstream of the heating air holes 26. What is important is that the profiles be interlocked when pre-softened and attached to the plastic sheet material when the side seals are formed. The distance between the locations where each of these four actions takes place is equal to the bag or package width. Referring now to a given location where a side seal area 34 is ultimately to be made, the interlocked profiles 18,20 are first pre-softened by hot air issuing from holes 26. Plastic sheet material then is moved one bag or package width, leaving the pre-softened area between vertical seal bars 30. Vertical seal bars 30 close and seal the male and female profile sections 18,20 to the plastic sheet material 10. The vertical seal bars 30 open and the plastic sheet material 10 advances another bag or package width. It will be appreciated that on a VFFS machine product is introduced into each bag or package through the fill tube prior to forming the final side seal for that bag. The areas of the male and female profile sections 18,20 previously pre-softened at holes 26 are again pre-softened at holes 28. Finally, after plastic sheet material 10 advances still another bag or package width, horizontal seal bars 32 clamp across the plastic sheet material 10 and interlocked male and female profile sections 18,20 at the pre-softened point to mash the profiles flat so that they fuse together and form a side seal area 34. Guide tubes 22 having holes 26,28 separated by different amounts may be substituted into the apparatus, or having holes 26,28 whose positions may be adjusted, and, having appropriately modified the locations of the vertical seal bars 30 and horizontal seal bars 32, plastic bags or packages of different widths may be manufactured. Modifications to the above would be obvious to those skilled in the art, but would not bring the method so modified beyond the scope of the appended claims. For example, the zipper may be disposed on the plastic sheet at some point other than at the lateral edges so that material is provided between the male and female profile thereby providing a tamper evident barrier outboard of the profiles in the final bag which must be ruptured before the profiles can be separated. Further, in some instances it may be desirable to provide guides upstream and downstream of hole 26 and/or hole 28 to separate and then reclose the zipper profiles before and after the presoftening hot air blast or to provide open zipper profiles and only close the profiles after presoftening.

Claims: A method for manufacturing plastic bags or packages wherein a longitudinally extending continuous plastic zipper having male and female profiles (18, 20) on interior surfaces of the plastic bag or package provides a resealable closure between two plies of plastic sheet material (10), said plastic sheet plies being welded together with a transverse seal (34) at preselected intervals separated by a distance corresponding to the width of the bags or packages being produced to thereby provide side seals separating said bags or packages, said method comprising the steps of: providing a continuous plastic zipper with male and female profiles (18, 20) between two plies of said plastic sheet material (10) which form the interior surfaces of said bag or package ; directing heat to a relatively short length of said continuous plastic zipper profiles (18, 20) whereby to presoften sections of said male and female profiles within said relatively short length of plastic zipper; and, making a transverse crosswise seam (34) across said two plies of plastic sheat material (10) and through said persoftened male and female profile sections (18, 20), characterized in that said directing heat step is accomplished by directing a hot air blast at the surfaces of said male and female profile sections (18, 20) within said relatively short length of said continuous plastic zipper to be softened, from between said two plies. The method in accordance with claim 1 wherein said male and female profiles (18, 20) are interlocked prior to directing heat thereon. The method in accordance with one of claims 1 or 2, wherein heat is directed to said relatively short length of said continuous plastic zipper (18, 20) at a plurality of locations. The method in accordance with one of claims 1 to 3, wherein said plastic sheet material (10) is folded into a generally tubular shape to provide said two plies of plastic sheet material and said hot air blost is directed at said surfaces of said male and female profile sections (18, 20) from within said generally tubular shape. The method in accordance with one of claims 1 to 4, wherein said hot air blast is directed against said surfaces of said male and female profile sections (18,20) simultaneously from more than one direction. The method in accordance with one of claims 1 to 5 wherein said plastic sheet material (10) and said continuous plastic zipper (18, 20) are separately provided and further comprising prior to the step of heating a relatively short length of said continuous plastic zipper, the steps of: attaching said male profile (18) of said continuous plastic zipper to one of said plies of plastic sheet material (10), attaching said female profile (20) of said continuous plastic zipper to the other of said plies of plastic sheet material. The method in accordance with claim 6 further comprising, prior to said attaching steps, the step of directing heat at said relatively short length of said continuous plastic zipper to presoften the male and female profile sections (18, 20) of said relatively short length of continuous plastic zipper prior to attaching said zipper to said plies of sheet material (10). The method in accordance with claim 7 further comprising interlooking said male and female profiles (18, 20) prior to said heat directing step. The method in accordance with claim 6 further comprising the step of interlocking said male and female profiles (18, 20) prior to said attaching steps. The method in accordance with one of claims 7 or 8 wherein said heat directing step is accomplished by directing a hot air blast directly at the surfaces of said male and female profile sections (18, 20) within said relatively short length of said continuous plastic zipper to be presoftened. The method in accordance with claim 10 wherein said plastic sheet material (10) is folded into a generally tubular shape and said hot air blast for preheating is directed at said surfaces of said male and female profile sections (18, 20) from within said generally tubular shape. The method in accordance with one of claims 10 or 11 wherein said hot air blast for preheating is directed against said surfaces of said male and female profile sections (18, 20) simultaneously from more than one direction. The method in accordance with one of claims 1 to 12 wherein the plastic sheet material (10) is moved incrementally in amounts equal in length to the width of the bags or packages being manufactured. The method in accordance with one of claims 1 to 13 wherein the male and female profiles (18, 20) are continuously guided by at least a guide tube (22) including an internal conduit (24) through which blasts of hot air are forcibly directed and at least a through hole (26, 28) permitting hot air to escape. The method in accordance with claim 14 wherein the male and female profiles (18, 20) are guided by two guide tubes (22). The method in accordance with one of claims 14 or 15 wherein the step of directing a hot air blast consists in directing hot air outside said guide tube(22) by way of at least two through holes (26, 28) provided in the guide tube. The method in accordance with of claims 14 to 16 wherein the step of directing a hot air blast consists in directing hot air outside said guide tube (22) by way of two through holes (26, 28) provided in the guide tube (22) respectively upstream and dowstream of longitudinally sealing means (30). The method in accordance with one of claims 1 to 17 wherein hot air is timely blasted.

Inventors: VAN ERDEN DONALD L, VAN ERDEN, DONALD L.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1994
Main classification: B29C65
IPC codes: B29C65, B31B19, B65B61, B65B9